1. Field of the Invention
This invention relates generally to head drive circuitry and in particular to an improved head drive circuit which includes open head or open cable detection. More particularly, the present invention relates to a magnetic tape recorder write head drive circuit which provides open head detection in a voltage or current mode write driver.
2. Description of the Related Art
Write head drive circuits having an H configuration are well known in the prior art. Such circuits are typically utilized in applications in which current is to be supplied in one of two directions to a load, such as a magnetic write recording head in a magnetic tape recorder or a magnetic disk drive. H write driver circuits are relatively fast and have generally low power dissipation.
Reliability and serviceability are highly desirable characteristics in magnetic data recording systems for a computer memory system. It is important to detect fault conditions that result in errors in the data recording process. A common fault in magnetic write recording systems is a poor or open wire connection (in the circuit card, write head coil or connecting cable) from the write head drive circuit to the inductive write head coil it drives. The open connection to the write coil renders the system inoperable, since data cannot be written to the magnetic media on the tape or hard disk. It is important to detect this fault condition and alert the user so that prompt remedial action can be taken.
A number of circuits and methods for detecting the open circuit condition are known to the art. U.S. Pat. No. 5,729,208 to H. Ogiwara describes a fault detection circuit integrated with the write driver using a comparator for comparing write head signals with a predetermined reference voltage level and generating differential comparison output signals. Latches coupled to the comparator use the write data as clock signals for latching differential comparison output signals just prior to polarity changes in the write head signals. A multiplexer coupled to the latches selects an output from the latches in response to the write data and generates an output indicative of an open circuit condition in the external write coil when the write head signals differ from an anticipated voltage reference level just prior to a predetermined polarity change in the write signal.
However, as data rates of magnetic recording systems have increased, the prior art solutions continue to have problems in reliably detecting faults. In particular, these circuits can indicate faults where none exist due to erroneous response to waveform transients.
Therefore, there is an ongoing need for an open write head detection circuit for magnetic recording systems that operates reliably at the highest write data rates.